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Colligative Properties

Colligative Properties. How does the solute change the properties of the solvent?. Consider aqueous solutions. Solvent = water. How do the properties of the solution compare to the properties of pure water?. Conductivity. Pure water does not conduct electricity. Some solutions do.

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Colligative Properties

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  1. Colligative Properties

  2. How does the solute change the properties of the solvent? • Consider aqueous solutions. • Solvent = water. • How do the properties of the solution compare to the properties of pure water?

  3. Conductivity • Pure water does not conduct electricity. • Some solutions do. • In order to conduct a current, a solution must contain ions. (MCPs) • Conductivity depends on the nature of the particle – Molecular solutes do not conduct.

  4. Colligative Properties • Depend on the number of particles in solution not on the type of particles. • Doesn’t matter if particles are ions or molecules. • Concentration of particles Does matter.

  5. What are some colligative properties? • Vapor Pressure Lowering • Freezing Point Depression • Boiling Point Elevation • Osmotic Pressure • The higher the concentration of solute particles, the larger the effect.

  6. Does it matter if the solute is ionic or covalent? • The number of particles will vary. • Ionic solutes will dissolve to produce positive and negative ions  more particles per mole of solute. • For covalent solutes, 1-to-1 relationship between moles of solute and moles of dissolved particles.

  7. C6H12O6 • Covalent • Dissolves as molecules C6H12O6(s) C6H12O6(aq) • 1 mole of sugar yields 1 mole of molecules

  8. NaCl • Ionic • Dissolves as ions • NaCl(s)  Na+(aq) + Cl-(aq) • 1 mole of salt yields 2 moles of ions. Get more particles from salt than sugar.

  9. MgCl2 • Ionic • Dissolves as ions • MgCl2(s)  Mg2+(aq) + 2Cl-(aq) • 1 mole of salt yields 3 moles of ions

  10. As a solute is added to a solvent, what happens to the freezing point & the boiling point of the solution? • The freezing point decreases & the boiling point decreases. • The freezing point decreases & the boiling point increases. • The freezing point increases & the boiling point decreases. • 4) The freezing point increases & the boiling point increases.

  11. Which solution containing 1 mole of solute dissolved in 1000 g of water has the lowest freezing point? • C2H5OH(aq) • NaCl(aq) • KOH(aq) 4) CaCl2(aq) Be careful! What if the question asked which solution has the highest freezing point?

  12. Of the following solutions, the one that will freeze at the lowest temperature contains 1 mole of nonvolatile solute dissolved in 1) 250 g of solvent 2) 500 g of solvent 3) 750 g of solvent 4) 1000 g of solvent Lowest fr. pt. means most concentrated.

  13. Which solute, when added to 1000 g of water, will produce a solution with the highest boiling point? • 29 g of NaCl • 58 g of NaCl • 31 g of C2H6O2 4) 62 g of C2H6O2  Mostconcentrated. About 1 mole of NaCl. 2 moles of ions. About 1 mole of C2H6O2. 1 mole of molecules.

  14. Which solution will freeze at the lowest temperature? • 1 g of NaCl dissolved per 100 g of H2O • 1 g of NaCl dissolved per 1000 g of H2O 3) 1 g of C12H22O11 dissolved per 100 g of H2O 4) 1 g of C12H22O11 dissolved per 1000 g of H2O

  15. Which solution will freeze at the lowest temperature? 1) 1 g of NaCl dissolved per 100 g of H2O 1 g  58.8 g/mole = 0.017 moles  0.034 moles of ions. 3) 1 g of C12H22O11 dissolved per 100 g of H2O 1 g  232 g/mole = 0.0043 moles of molecules

  16. Effect of NonvolatileSolute • Boiling Point Elevation • Freezing Point Depression • The more concentrated the particles, the bigger the effect!

  17. Applications of colligative properties • Salting roads in the winter time. • Using salted ice to make ice cream.

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